Currently, drugs or other fluids are often administered to patients intravenously through the use of a drug infusion pump. One commonly used type of drug infusion pump is a linear peristaltic drug infusion pump as shown in FIG. 1. This type of pump typically includes a peristaltic pump mechanism 12 having tube engaging members 13, and a detachable pressure plate 11. Pump mechanism 12 is part of a control module including control circuitry and data input structure, such as a keypad. The main surface of pressure plate 11 contains a plurality of oppositely disposed ribs 18 with a U-shaped channel between the ribs. A compressible tube 46 is attached to pressure plate 11 by threading the tube through an aperture 45 in one end of the pressure plate, through a loop-shaped pump anchor 28 and through a ring 47 at the opposite end of the pressure plate. Tube 46 is secured to pressure plate 11 and positioned in the U-shaped channels by use of ring 47 at one end and a restraint 44 at another end which is force-fit into aperture 45 of pressure plate 11. Together, tube 46 and pressure plate 11 form a tube/pressure plate assembly 50. Tube 46 is adhesively attached to restraint 44 and ring 47.
Tube/pressure plate assembly 50 is then attached to pump mechanism 12 by pump-securing extensions or hooks 24 on pressure plate 11 which engage a suspended pin assembly 14 having support plates 15 and pins 16 which are located on the bottom of pump mechanism 12. Pump anchor 28 located on pressure plate 11 engages a releasable engaging mechanism inside pump mechanism 12 to secure pressure plate 11 to pump mechanism 12. During use, tube engaging members 13 act in a predetermined sequence to draw a predetermined amount of fluid into tube 46 from a fluid reservoir and then expel the predetermined amount of fluid from tube 46 to the patient. The reservoir may be mounted to the pressure plate or it may be remote.
Because the amount of fluid introduced through tube 46 is controlled by the compression of tube 46, tube 46 is loosely fitted onto pressure plate 11 to allow the proper amount of compression to occur. To achieve a loose fit, tube 46 is only attached, such as by adhesive or solvent bond, to pressure plate 11 at opposite ends of pressure plate 11. Unfortunately, because tube 46 is loosely fitted, the tube can occasionally become misaligned with the U-shaped channel during the attachment of pressure plate 11 to pump mechanism 12 by the caregiver or patient. When misalignment occurs, tube 46 can be pinched between one or more of ribs 18 and pump mechanism 12 causing improper compression of tube 46 and a resulting improper delivery of fluids through tube 46. Misalignment may result in free flow, insufficient flow or no flow through tube 46.
As larger tubes are used to increase the amount of fluid flow per pump activation, the problems of misalignment are more likely to occur. The larger tubes will have a greater tendency to bow upward, increasing the chance of being pinched between a rib 18 and pump mechanism 12. Such upward bowing is caused in part by the increased flexibility of the tube and the tube entering and exiting the pressure plate at a vertical height lower than the main surface of the pressure plate.
A current commercial pressure plate 11 with compressible tube 46 by SIMS Deltec, Inc. of St. Paul, Minn., includes a large diameter portion 51, a first small diameter portion 52 attached to one end of large diameter portion 51, and a second small diameter portion 53 attached at the other end of large diameter portion 51. Large diameter portion 51 has an outer diameter of approximately 0.164 inches, while first and second small diameter portions 52, 53 each have an outer diameter of approximately 0.100 inches. Large diameter portion 51 has a wall thickness of approximately 0.032 inches and is capable of delivering approximately 50 microliters per activation of pump mechanism 12. The vertical drop at the ends of pressure plate 11 is about 0.050 inches. In some instances, tube misalignment is a problem for the prior system of FIG. 1.
There is a need in some cases to use tubes 46 with larger outer and inner diameters than the prior system of FIG. 1 to achieve a higher fluid flow. The larger tubes may be more flexible, and therefore more prone to bowing. Further, the larger tubes need to have more vertical drop at the ends of pressure plate 11 to avoid pinching off by pump mechanism 12. This may further increase tube bowing and the likelihood of misalignment.
Therefore, there arises a need for a pump pressure plate for use with a drug infusion pump which will automatically and reliably result in compressible tubes being aligned adjacent the pump mechanism. There is also a need for a more easily assembled pressure plate with compressible tube.